Upgrading primary manganese matte



April 20, 1965 R. c. KIRBY UPGRADING PRIMARY MANGANESE MATTE Filed Dec. 4, 1962 I iii/viz QQQ QQQQQQQQQQQ FIGJ IN VENTOR RAL PH 6. KIRB) ATTORNE Y5 United States Patent "ice UPGRADING PRIMARY MANGANESE MATTE Ralph C. Kirby, Silver Spring, Md., assignor to the United States of America as represented by the Secretary of the Interior Filed Dec. 4, 1962, Ser. No. 242,330 9 Claims. (Cl. 75-80) (Granted under Title 35, US. Code (1952), see. 266) The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

This invention relates to a method for refining primary manganese matte to obtain a low-iron manganese product.

Raw or primary manganese matte, which is refined according to the method of this invention, is produced by the first stage of the conventional two-stage matte smelting of manganiferous raw materials. In this first or primary smelting operation a suitable manganese raw material or ore is mixed with a sulfur-containing material such as pyrite or pyrrhotite, a reducing agent such as coke and the requisite amout of flux. This mixture of solids is heated in a suitable furnace at a temperature high enough to melt the constituents and produce a reaction whereby the manganese compounds in the starting materials are converted to manganese sulfide.

The manganese sulfide is contained in a separate liquid phase that forms the middle layer in the hearth of the furnace. This sulfide phase or matte contains, in addition to the manganese sulfide, iron sulfide in a proportion ranging to approximately twice the quantity of the manganese sulfide so that the melting point of the matte is below that of the manganese sulfide alone.

The gangue constituents form the top or slag layer above the matte in the hearth of the furnace. Iron from the raw materials that does not go to the matte phase is reduced to the metal which settles as the third or bottom liquid phase in the hearth of the furnace. By proper operation of the furnace the three liquid layers may be tapped from the furnace separately. Because the matte produced in this primary smelting operation includes iron sulfide as well as manganese sulfide, the quantity of man ganese lost to the slag is lowered greatly as compared to a matte consisting substantially of manganese sulfide alone.

In the second stage of the conventional smelting process manganese oxide is added to the manganese sulfideiron sulfide. matte from thefirst stage'to react with the sulfur and form the MnO-MnS eutectic. Since this procedure requires recycling of large quantities of the finished oxide product, the production of high grade manganese oxide by the conventional two-stage matte smelting process is economically unattractive.

It is therefore an object of the present invention to increase the economic attractiveness of the two-stage matte smelting process by substituting for the refining or secondary smelting operation a process that does not require the recycling of any finished oxide product.

Another object is to substitute a process alternate that requires less operating energy than the conventional refining operation.

It has now been found that these objectives may be achieved by a secondary smelting operation involving combined air-reducing agent treatment of the molten pri mary manganese sulfide-iron sulfide matte. The primary matte is thereby converted to two separate liquid phases consisting essentially of molten iron and molten refined matte that is a mixture of approximately equal portions of manganese sulfide and manganese oxide.

This refining action is accomplished by preferentially 3,1795% Patented Apr. 20, 1965 burning off the sulfur from the iron sulfide in the primary matte and simultaneously reducing the resultant iron oxide to iron metal with a reducting agent. The equations for these reactions, which are carried out at temperatures above the melting points of the starting primary matte and the final refined matte and iron metal, are:

where carbon is employed as the reducing agent. Because the free energy relationships are such that manganese sulfide is more stable than iron sulfide, sulfur will be removed from the iron first. The refining action is completed by burning off additional sulfur after all the iron has been removed so that approximately half of the manganese sulfide is converted to manganese oxide according to the equation:

In this way the low-melting eutectic of manganese sulfide and manganese oxide is formed; this facilitates handling since the eutectic has a desirably low melting temperature.

The over-all reaction for the refining step of the invention may be represented by the following equation:

Variations in the quantity of iron present in the primary matte will produce minor variations in quantites of reactants and products but the essential reaction is the same. Where the ratio of iron sulfide to manganese sulfide in the matte is 2: 1, the reaction is:

Following the refining treatment the two liquid phases or layers, iron metal and refined matte, are separated. The refined matte is subsequently cooled and calcined to produce a manganese oxide that is the desired product of the over-all matte smelting process.

The following examples will serve to more particularly describe the invention and illustrate the necessity of a reducing agent in the refining step. The general type of apparatus employed in the examples is illustrated in FIG. 1, and comprises a furnace consisting of outer wall 1 of fused silica (7 inch OD. x 12 inch height), fixed machined graphite crucible 2 (3% inchLD. x 9 /5 inch inside eight), 1 inch thick insulating carbon black 3, and high frequency induction coil 4 for supplying the desired temperature. Molten primary manganese matte 5 and coke particles 6 (where coke is used as the reducing agent) are contained in movable crucible 7, of machined graphite (2 /16 inch ID. x 8 inside height with A inch walls) or magnesia-lined machined graphite. Air is introduced by means of lance 8, of machined graphite (1 inch CD. with A inch wall) beneath the surface of the molten primary matte. A fused-silica tube was substituted in Examples 1 and 2 below to introduce air at the surface of the molten primary matte.

FIG. 2 illustrates separation of iron metal from refined manganese matte by pouring the refined matte from the movable machined graphite crucible into cast iron mold 9 where the iron metal 1% forms a button beneath refined matte 11.

The primary matte feed used in the examples contained 24.5 percent manganese and 37.9 percent iron. Its molecular formula was approximately MnS-LSFeS and melting point was between 1350 and 1400 C. The effectiveness of the conversion was gauged by the quantity of iron metal produced, which upgraded the manganese content of the matte.

Example 1 Example 2 In this example a graphite crucible was employed, without the magnesia lining. The surface of the molten matte was blown through a fused-silica tube with 177 liters (S.T.P.) of air (equivalent to 53 grams of oxygen) for 15 minutes No metal was formed even though the melt was in contact with the graphite crucible walls.

Example 3 In this example a graphite crucible was employed with a graphite pipe for the lance. After blowing (with lance extending below the surface) :for 25 minutes with 84 liters (S.T.P.) of air, 3 percent of the iron present in the melt was recovered as metal. Iron recovery based on oxygen fed was 0.13 gram Fe/gm.

Example 4 As seen in the previous example, carbon present at the melt-air interface in the form of the hot graphite lance produced iron metal while, as shown by Example 2, the carbon of the graphite crucible, which was not at the meltair interface, had no effect on the converting. In order to obtain a larger distribution of carbon at the melt-air interface, 25 grams of minus-10, plus-1 r mesh coke was added to the same primary matte charge as that employed in the previous examples. Using a submerged graphite lance, as shown in FIG. 1, the melt was blown with 138 liters (S.T.P.) of air for 25 minutes. Fifteen percent of the iron in the charge was recovered as metal. Iron recovery based on oxygen fed was 0.35 gram Fe/grn. 0 The melt was very fluid when poured and produced a clean separation of metal from matte. The manganese-to-iron ratio of the matte was raised from 0.64 to 0.76 while the manganese content of the metal was less than one percent.

Example 5 In this example natural gas was used as the source of carbon in place of the coke of the previous examples;

thermal cracking of the methane to carbon and hydrogen takes place at the conversion temperature. The feed matte was the partially refined mattes from the previous two examples which has been blown with air. The procedure was thus equivalent to an alternate blowing with air and natural gas. The melt was blown with 23 liters (S.T.P.) of natural gas for minutes with the submerged graphite lance. Eight percent of the iron in the charge was recovered as the metal. Iron recovery based on natural gas was 0.63 gm. Fe/grn. CH The manganese-to-iron ratio of the matte was raised from 0.70 to 0.82. It was found, however, that more of the melt was blown from the crucible when natural gas was employed than in the previous examples using air or oxygen.

Example 6 In this example primary matte was blown with natural gas using the submerged graphite lance. The blowing period was tripled over the previous example by covering the crucible with sheet mica to stop most of the blowout. The melt was blown for 40 minutes wit-h 68 liters (S.T.P.) of natural gas. Twenty percent of the iron charged was recovered in the metal phase. Though the manganese grade of the matte was improved, the manganese-to-iron ratio being raised from 0.64 to 0.88, iron recovery based on natural gas was 0.40 gm. Fe/ gm. Ch as compared to 0.63 gm. Fe/ gm. CH in Example 5.

Though the reducing agent (coke or methane) and the air were introduced separately in the examples, other means may be employed; for example, where the reducing agent is coke or coal, it may be added to the air stream in powdered form in such a way as to become entrained therein, the resultant stream of air and carbon having the properties of a single fluid. Also, as indicated in Example 5, air and methane may be alternately blown into the fused matte. The size of the coke particles is not critical and may vary widely depending on the nature of the primary manganese matte, size of the charge, method of introduction of air, etc. Introduction of air may also be accomplished in a variety of ways, as at the surface of the molten matte or beneath the surface. The rate of air flow and the amount of air is also not critical and the optimum value can best be determined experimentally.

The apparatus employed in the invention may be varied widely according to the amount and type of primary matte to be treated, method of introduction of the air or oxygen and reducing agent, degree of automation desired, etc. In the examples a small scale apparatus was employed; for large scale operations a side blown converter or a converter using a top-blowing lance would usually be employed. Though a high frequency induction coil was employed in the examples to heat the crucibles in order to maintain the matte in a molten condition, for large scale operations such heating is not necessary since the heat capacity of the charge is sufficient to maintain it in a molten condition. The blowing reaction itself does not require heat since the air-carbon converting reaction for the primary manganese matte is exothermic, thus requiring less operating energy than conventional refining operations.

The method of separating ir-on metal and refined matte Will also depend on the size of the operation. In a small scale operation, as employed in the examples, the separation is accomplished by pouring the melt of the refined matte and iron metal into a conically shaped cast iron mold (FIG. 2) where the melt solidifies rapidly but not before the iron settles to the bottom. When the mold is emptied, the iron metal is found as a button at the bottom of the cone. 7

In larger operations a method of separation based on slower freezing of larger quantities of molten material is used. Two ladles in series receive the melt as poured from the converter. The first is large enough to hold only the iron formed in the react-ion; the iron settles out in this ladle while the rest of the melt, the refined matte, overflows into the second ladle.

Results of the examples show that the combination of air and reducing agent is essential if optimum results are to be achieved, i.e., if a maximum formation of iron metal is to be achieved. Any iron metal which forms represents iron removed from the matte, thereby raising the manganese-to-iron ratio of the matte and thus producing a high grade manganese product. The iron separated is also recovered as a by-product.

It is thus seen that applicant has developed a method of refining primary manganese matte by blowing with air to burn off a major part of the sulfur while at the same time reducing the iron oxide formed to iron metal by means of a reducing agent. -It is apparent that this method obviates the necessity. of recycling manganese oxide as in conventional refining processes and results in a more efficient and economical process.

What is claimed is:

1. A method for refining primary manganese matte consisting essentially of manganese sulfide and iron sulfide in a ratio of manganese sulfide to iron sulfide of from about 1:1 to about 2:1 comprising treating the molten primary matte with an oxidizing gas from the group consisting of air and oxygen and a reducing agent from the group consisting of coke, coal andnatural gas to form two separate liquid phases consisting of molten refined manganese matte as one phase and molten iron metal as the second phase, and separating the two phases to recover refined manganese matte.

2. Method of claim 1 in which the oxidizing blown into the molten primary matte.

3. Method of claim 1 in which the oxidizing oxygen.

4. Method of claim 1 in which the oxidizing gas is air.

5. Method of claim 1 in which the reducing agent is coke.

6. Method of claim 5 in which the coke is introduced into the molten primary matte in coarsely crushed form.

7. Method of claim 1 in which the reducing agent is coal.

8. Method of claim 1 in which the reducing agent is natural gas.

9. Method of claim 1 in which the oxidizing gas is gas is gas is added in an amount to oxidize about half of the manganese sulfide to oxide in order to form manganese sulfidemanganese oxide eutectic.

References (Iited hy the Examiner UNITED STATES PATENTS 9/44 Knickerbocker 75-8O X OTHER REFERENCES BENJAMIN HENKIN, Primary Examiner.

DAVID L. RECK, Examiner. 

1. A METHOD FOR REFINING PRIMARY MANGANESE MATTE CONSISTING ESSENTIALLY OF MANGANESE SULFIDE AND IRON SULFIDE IN A RATIO OF MANGANESE SULFIDE TO IRON SULFIDE OF FROM ABOUT 1:1 TO ABOUT 2:1 COMPRISING TREATING THE MOLTEN PRIMARY MATTE WITH AN OXIDIZING GAS FROM THE GROUP CONSISTING OF AIR AND OXYGEN AND A REDUCING AGENT FROM THE GROUP CONSISTING OF COKE, COAL AND NATURAL GAS TO FORM TWO SEPARATE LIQUID PHASES CONSISTING OF MOLTEN REFINED MANGANESE MATTE AS ONE PHASE AND MOLTEN IRON METAL AS THE SECOND PHASE, AND SEPARATING THE TWO PHASES TO RECOVER REFINED MANGANESE MATTE. 